Telescoping lattice towers are generally made up of multiple lattice sections that telescope within each other as shown in FIG. 1. The telescoping tower 10 depicted in FIG. 1 includes a base section 12 and two upper sections 14 and 16. Section 14 nests into base section 12 and section 16 nests into section 14.
The most common method used to extend and retract the sections 14 and 16 is by means of suspension cables made from wire rope. The base section 12 typically has a hand operated or motorized winch 18 to hoist the second lower most section 14 of the tower. All sections above the second lower most section 14 are cabled in a manner to respond to the movement of the second lower most section 14 relative to the base section 12 resulting in all sections telescoping simultaneously in both the extend and retract motions.
In the application of telescoping lattice towers with payloads having large projected wind sail areas, or if it is necessary to maintain stiffness in the extended tower, guy cables are often used. When an extended tower is equipped with guy cables, the result is larger vertical or axial loads from both the initial pre tensioning of the guy cables and resultant vertical loads from elevated wind speeds acting against the wind sail area(s).
When axial loads are increased, the loads in the lift or suspension cables also increase. In the case of the upper telescoping sections, multiple lift cables can be installed to increase the axial load capacity of the tower. However, this is not easily accomplished for the main lift cable or the winch cable.
In many applications, a lock system is incorporated at the interface of the base section and second lower most section to remove the main lift cable from the axial load path. The locks are typically located to lock the base section and second lower most section when the tower is at full extension.
FIG. 2 is a diagram showing a typical prior-art lock arrangement at the interface of the base section 12 and second lower most section 14 to remove the main lift cable from the axial load path. A lock base 20 includes opposed faces 24 each having a horizontal slot 26 and is fixed to each of the vertical members of the base section 12. A horizontally-oriented plate 28 is coupled to actuating arm 30 and is pivoted about pivot point 32.
To lock the second most lower section 14 to base section 12, the tower 10 is raised so that the bottom of the second most lower section 14 is positioned above slots 26 and the arm 30 is rotated to move the plate 28 through slots 26 in the opposing faces of the lock base 20 so that plate 28 is positioned under the bottom member 34 of the second most lower section 14. The tower 10 is then lowered until the bottom member 34 of the second most lower section 14 rests on plate 28, which then carries the vertical load of all of the upper sections of the tower 10 because it is captured in slots 26. FIG. 2 shows the lock plates 26 in the locked position.
While this solution addresses the problem when the tower is fully extended, there is a need for a system for locking the base section to the second lower most section at intermediate heights to allow the tower to be guyed at different elevations as opposed to only fully extended.